The present invention relates to a transmission including motors and differential mechanisms, and a vehicle and a bicycle using the same.
A hybrid car utilizing a drive force of a motor has been known as a drive system aimed at reducing a fuel consumption of an engine. Various kinds of hybrid cars have been proposed, for example, a series hybrid type, a parallel hybrid type, and a series/parallel hybrid type using two motors and one planetary gear. Concretely, Japanese Patent Laid-open No. Hei 7-135701 discloses a method in which a drive force of an engine is inputted in a planetary gear and a vehicle is driven by a drive force obtained by an output shaft of the planetary gear, wherein the drive force is controlled by a generator. In this method, since part of the energy of the engine is used for generating electric energy by the generator and the drive force of the engine is assisted by the motor connected to the output shaft, the engine can be usually driven in a high-efficiency/high-torque region and the vehicle can attain a transmission function. The same principle has been also disclosed in Japanese Patent Laid-open Nos. Sho 49-112067 and Sho 58-191364. This known method disclosed in the above documents is hereinafter referred to as "a first method".
As disclosed in Japanese Patent Laid-open No. Sho 60-95238, there has been proposed a method in which a drive force of an engine is transmitted to right and left drive wheels via planetary gears controlled by motors, respectively. This method is hereinafter referred to as "a second method".
As disclosed in Japanese Patent Laid-open No. Sho 57-47054, there has been proposed a method in which a plurality of planetary gears are driven by motors respectively and a drive force is outputted from the selected one of the plurality of planetary gears, so that the optimum drive of the motors can be performed in accordance with the operational point of the vehicle at all times. This method is hereinafter referred to as "a third method".
As disclosed in "Alternative Cars in the 21st Century -A New Personal Transportation Paradigm-, Robert Q. Riley, Published by Society of Automotive Engineers, Inc., 400 Commonwealth Drive Warren dale, Pa. 15096-0001, U.S.A., p.149-P153", there has been proposed a transmission using a continuously variable transmission CVT in combination with a planetary gear. In this method, since the vehicle can be stopped while the engine is rotated, without using of any clutch, by setting a speed varying ratio of the continuously variable transmission CVT at a specific value, it is possible to smoothly start the vehicle only by controlling the speed varying ratio of the continuously variable transmission CVT. This method is hereinafter referred to as "a fourth method".
The first method, however, has a problem. Since electric energy is generated by the generator and the vehicle is driven by the motor for realizing the transmission function, a loss in electric energy occurs. As a result, although the engine can be always driven at an operational point being good in efficiency, the efficiency of the entire vehicle is reduced correspondingly to the loss in electric energy.
The second method, in which the planetary gears are provided for the right and left different output shafts, respectively, has a configuration obtained by extending the configuration of a usual parallel hybrid car to the right and left wheels. As a result, the second method requires the input/output of electric energy for realizing the speed varying operation, and therefore, this method has the same problem as described above.
The third method has a configuration obtained by extending the configuration of the first method. As a result, this method has the same problem as described above in terms of the loss in electric energy.
The fourth method has a problem that since the engine must be always rotated for driving the vehicle, there is a limitation in reducing the fuel consumption per unit running distance over a period, in which the engine is driven, including a stop of the vehicle.